FIG. 1 is a front view of a conventional manganese dry battery, partially in cross section. As shown in FIG. 1, in the conventional manganese dry battery, a separator 3 is positioned inside of a negative electrode zinc can 6, in which a positive electrode material mixture 2 is inserted. A top surface of the positive electrode material mixture 2 is covered with kraft board 5 having an aperture in the center for inserting therein a positive electrode carbon rod 1, and the carbon rod 1 is inserted in the center. This manganese dry battery includes bottom paper 4, a negative electrode terminal plate 8, a seal ring 9, a heat-shrinkable tube 10, a positive electrode terminal plate 11, an insulating ring 12 and an outer jacket can 13.
In order to block (seal) the inside of the dry battery from the outside, the carbon rod 1 is inserted in an aperture of a sealing part 7 made of a thermoplastic resin such as polyethylene so that the both are held firmly and hermetically and an opening or an opening edge of the negative electrode zinc can 6 is engaged into the sealing part 7 to establish a fit between them.
Further, a sealant 14 such as asphalt or polybutene is applied to a part where the sealing part 7 holds the carbon rod 1 and a part where the sealing part 7 is fitted with the negative electrode zinc can 6 to ensure the sealing.
However, if the filling amount of the positive electrode material mixture 2 is increased to improve discharge property, the positive electrode material mixture 2 in the battery increases in height. Then, the kraft board 5 positioned on the top surface of the positive electrode material mixture 2 approaches the sealing part 7 and may come into contact with the sealing part 7 as shown in FIG. 2 if the positive electrode material mixture 2 expands during storage or discharge of the battery. FIG. 2 is a front view of another conventional manganese dry battery, partially in section.
Then, due to the contact between the kraft board 5 and the sealing part 7, a sealant 14′ applied into a groove lying in an innermost periphery portion of the sealing part 7 and between the sealing part 7 and the positive electrode carbon rod 1 is absorbed into the kraft board 5. The groove has a substantially triangular shape in vertical section and is filled with the sealant 14′.
There are lots of microscopic asperities on the surface of the positive electrode carbon rod 1. Accordingly, if the sealant 14′ is absorbed into the kraft board 5, there arise problems in that a degree of sealing is reduced and an electrolyte may possibly leak out of the battery.
The opening of the negative electrode zinc can 6 is fitted with an outer periphery portion (outer side portion) of the sealing part 7 as shown in FIG. 2, with certain space kept between the kraft board 5 and the outer periphery portion even if the kraft board 5 contacts the sealing part 7. However, in the case where the positive electrode material mixture 2 expands as described above to bring the kraft board 5 into contact with the outer periphery portion of the sealing part 7 fitted with the opening of the negative electrode zinc can 6, a sealant 14″ applied to the fit portion is also absorbed into the kraft board 5. As a result, as in the case of the part between the positive electrode carbon rod 1 and the sealing part 7, the electrolyte may leak from a gap between the opening of the negative electrode zinc can 6 and the sealing part 7.
In view of these problems, an object of the present invention is to provide a manganese dry battery with excellent leak-proof property, in which the shape of the sealing part is improved such that leakage of the electrolyte does not occur even if the size of the positive electrode material mixture is increased to meet a demand for improvement in discharge property.